1. Field of the Invention
The present invention relates to an organic light emitting display (OLED) and a method of fabricating the same, and more particularly, to an OLED having a pixel electrode structure which permits laser-repairing and minimizing damage of the device, and a method of fabricating the same.
2. Description of the Related Technology
Among flat panel displays (FPDs), an organic light emitting display (OLED) is an emissive device that has a wide viewing angle and a fast response speed of about 1 ms or less. Also, the OLED can be fabricated to a small thickness at low costs and has good contrast, and thus has attracted much attention as a next generation flat panel display.
Such an OLED typically includes an anode, a cathode and an emission layer interposed between these two electrodes. When a voltage is applied between the anode and the cathode, holes and electrons move to the emission layer, and are recombined in the emission layer to emit light.
In an OLED, dark spots which do not emit light even though a voltage is applied thereto may be created by a short circuit between the anode and cathode.
FIG. 1 is a photograph showing an OLED having a plurality of unit pixels. Referring to FIG. 1, a dark pixel d that does not emit light may cause the OLED to malfunction.
FIGS. 2A to 2C are micrographs, taken with a scanning electron microscope, of a region in which a dark pixel is formed. Referring to FIGS. 2A to 2C, the causes of the dark pixel can be seen.
As shown in FIG. 2A, an emission layer may be shorted due to an error during its fabrication process. It can be seen that the dark spot corresponds to a region where the emission layer is shorted.
The dark spot may also be caused by a particle created during the formation of the emission layer or a cathode as shown in FIG. 2B. The dark spot may also result from a failure of an underlying layer pattern as shown in FIG. 2C. In addition, while driving the OLED, the dark spot may occur due to concentration of electric field in a potential failure part.
In an active matrix (AM) OLED, the dark spot defect occurs due to a local short circuit between the anode and the cathode. One of the problems of such a dark spot is that as time elapses, the dark spot grows in size until finally a unit pixel having the dark spot becomes a dark pixel which cannot be not turned on. Thus, the reliability of the OLED deteriorates.
Conventionally, attempts were made to fix dark spots through a laser repair process in which a laser beam is applied to impurities such as particles to remove the impurities. The laser beam removes impurities, but it may also damage a region surrounding the impurities. Such damage can provide a path for moisture or oxygen to infiltrate to pixels, thereby reducing the lifespan of the OLED.